In a known personal authentication apparatus for preventing an unauthorized person from approaching a building or a specific place within the building, a known personal authentication apparatus for preventing an unauthorized person from operating an apparatus, such as an information processing apparatus, or a known personal authentication apparatus for identity verification in electronic commerce using Internet, a personal authentication apparatus using a biometrics authentication system that performs identity verification using a biological feature of a person without using a key or a personal identification number is provided (for example, refer to Patent Document 1).
In addition, in personal authentication apparatuses using the biometrics authentication system, a system that performs authentication by a fingerprint, a system that performs authentication by a voiceprint, a system that performs authentication by a face, and the like are used.
A system that performs authentication by a face, that is, a face recognition system is configured to perform recognition by extracting a feature value of a face from a facial image and comparing the similarity with a feature value registered beforehand when face recognition is performed. In this case, the positions of both eyes and the mouth are detected and thereby face recognition is performed by template matching processing in which a modified template is set as a feature value of a face. At this time, it is a prerequisite that the facial image includes both eyes and the mouth. When either detection of both eyes or detection of the mouth has failed, it is determined that a face does not exist in the image and an alarm is given.    Patent Document 1: JP-A No. 2000-163600